1. Field of the Invention
Exemplary embodiments of the present invention relate to a TOF camera for a vehicle, and more particularly, to a TOF camera for a vehicle, which can increase a detection range by using a plurality of laser diodes as light sources, and a method for driving the same.
2. Description of the Related Art
In general, a TOF (Time of Flight) camera detects an object by using delay of a phase and the like generated when light modulated with a predetermined frequency is reflected and returned from the object, and is used in a topographical survey field, a gesture control field of an object, a rear-end collision prevention device of a vehicle, and the like.
According to the operation principle of the TOF camera, the TOF camera includes a light source that emits light having a predetermined center wavelength, and the light source modulates emitted light with a predetermined frequency and irradiates the light to an object to be detected.
Then, the light irradiated to the object is reflected and is returned to the TOF camera, and the TOF camera detects the returned light by using a sensor embedded therein.
In this case, the TOF camera compares a phase of the emitted light with a phase of the light reflected and returned from the object, thereby calculating the distance to the object.
FIG. 1 is a block diagram of a general TOF camera.
As illustrated in FIG. 1, the TOF camera may include a light receiving unit 10 that receives a reflection light reflected from an object 30 and a light emitting unit 20 that irradiates modulated light to the object 30.
The light emitting unit 20 controls each light emitting element 22 by using a modulation signal provided from the light receiving unit 10, thereby irradiating the modulated light to the object 30.
Then, the modulated light is reflected from the object 30 and is collected in a light receiving element 14 through a light receiving lens module 12 of the light receiving unit 10.
The light receiving element 14 converts light energy into electrical energy and transfers the electrical energy to a signal processing module 16, and the signal processing module 16 determines the distance to the object by using a phase difference between the input signal and the modulation signal.
However, since the existing TOF camera uses a light emitting diode as a light source, there is a problem that a detection range is short.
Accordingly, in the case of using a laser diode as a light source instead of the light emitting diode, since the laser diode can obtain relatively strong power as compared with the light emitting diode, it is possible to obtain an improved detection range when using the same current.
FIG. 2 is a graph obtained by comparing optical power characteristics of a light emitting diode and a laser diode with each other.
As illustrated in FIG. 2, it can be understood that the laser diode can obtain relatively strong power as compared with the light emitting diode when using the same current.
Accordingly, as compared with the light emitting diode, the laser diode has characteristics in which a detection range is improved and it is tolerant to external light due to a narrow wavelength band.
Since the TOF camera basically operates a light emitting element based on a modulation signal, it is necessary to operate a laser diode in a pulse mode.
However, a pulsed laser diode has high peak power but requires a long cooling time for removing generated heat at the time of light emitting.
Therefore, due to a long duty cycle of the laser diode, it may be difficult to operate the laser diode according to a fast modulation time of the TOF camera.